I never checked for vibration in gear with out the car moving, so I just did that. In Drive and reverse holding the brake so the car cannot move and bringing the RPM's up against the converter, I get about the same vibration that maxes at 1250 RPM. Subjectively it is very similar to what I see and feel in neutral and park. So if during this test the only thing turning is the engine and the torque converter, it seems to rule out any internal transmission problem. I guess the pump is also running? Am I thinking this through correctly?

I rechecked the firing order and plug wire connections. All checked out fine. I have 15" of vacuum at 750 rpm idle and the vacuum is steady. Inspected the trans mount pretty carefully and did not see any issues with the rubber or metal. It is a new aftermarket one and is not ideal, but better than the old one that came with the car. IIRC, the metal bracket on the new mount was pretty flimsy, so I removed the rubber insert with the metal sleeve that surrounds it and put it in the original metal bracket.

Yes, the car set for probably a couple of weeks between the last time I drove it and did not notice any vibration and when I first noticed the vibration. The day I first noticed the vibration the beginning of the drive seemed fine and then after probably 10 minutes of driving I began to notice the vibration. I do not recall hearing anything like something that might have come loose, but I really was not paying real close attention since it was a nice day and I was just enjoying a drive.

When I rebuilt the trans, I replaced the pump bushing with a Babbitt bushing I sourced from A&A. I thought I had some measurements of the clearance, but cannot find them so maybe I did not take any measurements. It was the early narrow bushing. I don't see any trans fluid leaks anywhere.